This invention relates generally to surgical instruments, particularly with respect to improvements in devices for cutting or piercing patient tissue while minimizing or eliminating bleeding. More specifically, this invention relates to an improved surgical knife for hemostatic cutting of patient tissue, wherein the improved surgical knife has a relatively hard and long-wearing surface for contacting patient tissue substantially without sticking while providing significantly improved transfer of electrical energy for electrocauterizing patient tissue.
Electrosurgical instruments such as scalpels, knives and the like are well known in the medical arts for incising soft patient tissue with concurrent transmission of electrical energy to the contacted tissue to cauterize small blood vessels and thereby minimize bleeding. Such devices utilize a relatively high frequency electrical current passed through the typically stainless steel and conductive tool structure to disrupt blood vessels by vaporization and/or cauterization at the point of cutting contact. The electrical energy provides a source of localized heating which imparts thermal damage to contacted patient tissue and cellular layers in a manner causing denaturizaton of proteins and sealing of blood vessels. In this regard, to achieve a smooth-edged incision conducive to rapid postsurgical healing with minimal scar formation, it is highly desirable for the electrical energy to be transmitted to the contacted patient tissue in a closely controlled manner and with a substantially uniform current density in order to minimize or prevent tissue and blood vessel damage beyond the immediate area of the contacted tissue. Conversely, the absence of a closely controlled and substantially uniform current density undesirably produces uneven localized thermal tissue damage, resulting in an irregular or ragged incision margin which heals more slowly and with a higher incidence of aesthetically unappealing scar tissue. For examples of electrosurgical instruments of this general type, see U.S. Pat. Nos. 4,248,231; 4,232,676; 4,161,950; 4,033,351; 4,333,467; 4,314,559; 4,481,057; and 3,913,583.
While such electrosurgical tools have proven to be effective to control bleeding in the course of surgical procedures, problems have been encountered with respect to sticking of soft incised tissue to the surgical instrument. More particularly, charred and necrosized tissue and cells can be generated by localized excessive thermal heating, wherein such tissue and cells tend to adhere to the surgical instrument such as the cutting edge of a surgical knife. Unfortunately, the presence of such tissue and cells on the working surface of the instrument interferes with subsequent hemostatic cutting by disrupting the current field and correspondingly reduce the efficiency and efficacy of the instrument. To combat this problem during surgery, it is necessary for the surgeon to frequently replace the electrosurgical knife or the like with a clean instrument, or alternately to frequently interrupt the surgical procedure while the instrument is wiped clean with an abrasive pad or the like. In either case, the surgical procedure is prolonged and the overall risk and cost of patient care are thus increased.
In the past, significant design efforts have been directed to improvements in electrosurgical knives and the like, with a view toward providing improved transmission of electrical energy to patient tissue in a manner to reduce sticking of soft tissue to the cutting surface. In general, such design efforts have envisioned non-stick surface coatings, as described, for example, in U.S. Pat. Nos. 4,314,559; 4,333,467; 4,161,950; 4,481,057; 4,785,807; and 7,876,110. Such non-stick surface coatings have typically comprised a polymeric material such as a fluorinated hydrocarbon (e.g., polytetrafluoroethylene (PTFE, commonly known as Teflon)) for increasing the lubricity of the tool surface. These non-stick surface coatings have enabled an improvement in electrocautery knives to be obtained. Typically, however, such fluoropolymer coatings exhibit dielectric properties which may impair the efficiency and efficacy of hemostatis. In particular, U.S. Pat. Nos. 4,785,807 and 4,876,110 disclose a dual layer dielectric insulating coating designed for achieving capacitive coupling of the electrosurgical radio-frequency (RF) energy to the patient""s flesh. In these two patents, at least the outer layer of the coating comprises a fluorinated hydrocarbon material having a thickness which is sufficiently thin to permit capacitive coupling of the RF electrical energy through the coating to the tissue being cut. In addition, such fluoropolymer coatings may exhibit a tendency to release from the tool substrate due to formation of microporosity, delamination and/or abrasive wear, thus exposing underlying portions of the tool substrate to direct tissue contact and related sticking problems. Such release of the coating from the tool substrate may be enhanced by the thermal heating which occurs during normal intended use.
It is believed that such non-stick polymer coatings have the potential to undergo morphological changes during use, eventually leading to delamination failure. See Konesky, xe2x80x9cPorosity Evolution in Electrosurgical Blade Coatingsxe2x80x9d, p. 249, Proc. of the Materials Research Society Symp., Vol. 550, Boston, Mass., November 1998. More specifically, such polymeric coatings are typically provided with a very thin coating thickness on the order of about 40-150 microns, wherein the coating has strong dielectric properties. A coated electrosurgical knife of this type is believed to develop a series of holes or voids of varying size and distribution in the insulative non-stick coating, wherein these holes or voids lead to nonuniform variations in the capacitive transmission of the electrical energy to the contacted patient tissue to create localized excess heating, excess tissue damage, undesired irregular sticking of tissue to the knife, and further degradation and delamination of the non-stick coating. Indeed, when microporosity extends from the outer surface of the fluorinated hydrocarbon coating to the metal tool substrate, some direct ohmic electrical energy transfer may occur, which might exacerbate the nonuniform or inhomogeneous RF electrical energy transfer to the tissue.
Additionally, the soft incised and cauterized tissue may stick to the outer surface of the electrosurgical tools with the coating as disclosed in U.S. Pat. Nos. 4,785,807 and 4,876,110. The inherent microporosity of the coating disclosed in these patents presents a higher surface energy which may promote tissue sticking.
U.S. Pat. No. 4,314,559 discloses an alternative coated electrosurgical knife having a first conductive coating applied to the knife substrate, and a second outer non-stick polymeric coating applied to fill the microscopic interstices of the first coating in an attempt to provide improved adherence of the non-stick coating to the knife. The two layer coating essentially provides a conductive underlayer with a large plurality of microscopic conductive islands exposed through gaps in the overlying non-stick outer layer. This structure inherently transmits the electrical energy to the patient tissue in a nonuniform manner with spatially varying electrical and thermal conductivity, resulting in excess heating damage of tissue and consequent tissue sticking to the knife blade. Moreover, the small pores in the outer coating are a potential source of electrical discharge arcs which can pose a serious risk of fire in a surgical operating room environment.
There exists, therefore, a need for further improvements in and to electrosurgical instruments such as an electrosurgical knife and the like, wherein the instrument is designed to transmit electrical energy to patient tissue in a closely controlled and substantially uniform manner consistent with optimized hemostatic cutting of soft tissue, substantially in the absence of sticking of such patient tissue to the instrument. Moreover, there exists a need for such electrical instruments having an improved non-stick surface coating designed for relatively long service without delamination failure. The present invention fulfills these needs and provides further related advantages.
In accordance with the invention, an improved electrosurgical instrument such as an electrosurgical knife is provided for hemostatic cutting of soft patient tissue in the course of a surgical procedure. The electrosurgical instrument comprises a conductive substrate such as a knife blade of stainless steel having an improved substantially non-stick and electrically conductive coating applied to at least the portion thereof for contacting patient tissue. The improved coating comprises a combination of conductive, non-stick and hardening agents to exhibit beneficial properties of improved coating stability, improved electrical and thermal conductivity, improved wear resistance, and a relatively low surface coefficient of friction (high lubricity).
More particularly, the improved coating comprises multiple coating layers applied to the instrument substrate in a sequence for substantially optimized adherence thereto, wherein each of the coating layers is loaded with a matrix of conductive material such as conductive particles. Alternatively, the use of a selected organic additive which can be homogeneously dissolved on a molecular scale and can pyrolize during the subsequent baking process to form a carbon residue can also be advantageously employed. The multiple coating layers include at least one base coat applied to the substrate, wherein the base coat includes the conductive material in an aqueous suspension of a hydrocarbon such as polyamide imide or polytetrafluoroethylene (PTFE) and a conductive agent. The multiple coating layers further include an outer coat loaded with the conductive material and the hardening agent, in combination with an aromatic hydrocarbon and a fluorinated hydrocarbon.
In one preferred form, the improved coating comprises a base coat, a mid coat and a top coat. The base coat preferably consists of a liquid suspension containing de-ionized water, chromic acid, and a hydrocarbon binder such as polyamide imide solution or an aqueous suspension of a fluorinated hydrocarbon such as polytetrafluoroethylene (PTFE), selected for intimate and stable bonding with the instrument substrate, wherein the suspension is loaded with conductive material such as graphite or a semi-conducting oxide particles having a particle size of about 10-20 nanometers and in a proportion of about 25-35% by weight. This base coat is applied to the substrate by spraying or dipping, allowed to dry, and then subjected to heat for a time and temperature sufficient to cure the base coat thereon.
A second or mid coat is then applied, consisting of a liquid carrier such as de-ionized water loaded with the same conductive material in a proportion of about 20-35% by weight in combination with an aqueous dispersion of a fluorinated hydrocarbon binder such as a fluorinated ethylene propylene copolymer (FEP) or perfluoroalkoxy (PFA) having a solids loading of about 20-80% by weight. This second coat is applied over the base coat by spraying or dipping, and allowed to dry.
A third or outer top coat is prepared by adding the hardening agent, for instance ceramic particles such as titania or alumina or mica in a particle size of about 10-20 nanometers, to the liquid suspension prepared in the same manner as the mid coat, with the ceramic constituent being added in a proportion of up to 30% by weight. Alternatively, an organic agent such as an acrylic polymer may be employed. This top coat is applied over the second coat by spraying or dipping, allowed to dry, and then subjected to a final heat step sufficient to produce a hard conductive composite coating on the substrate. In an alternative preferred form, this top coat may be applied to the base coat, with the mid coat being omitted.
Other features and advantages of the invention will become more apparent from the following detailed description, taken in conjunction with the accompanying drawings which illustrate, by way of example, the principles of the invention.